The invention generally relates to a method and apparatus to automatically recover well geometry from low frequency electromagnetic signal measurements, and more particularly, the invention relates to a method and apparatus to automatically recover receiver and/or transmitter positions for purposes of performing crosshole electromagnetic tomography.
Crosshole electromagnetic tomography is an example of a conventional technique that may be used to characterize an oil reservoir. In this technology, electromagnetic waves typically are communicated between two wellbores that are in proximity to the oil reservoir of interest. The electromagnetic waves are altered by the reservoir in a manner that identifies certain properties of the reservoir. Therefore, measurements of electromagnetic waves that are communicated through the reservoir may be processed to develop a two or three dimensional image, or survey, of the reservoir.
A typical application of crosshole electromagnetic tomography involves the use of a receiver tool that is run into one wellbore and a transmitter tool that is run into another wellbore. The transmitter tool, as its name implies, transmits electromagnetic waves, and the receiver tool performs measurements of the resulting received electromagnetic waves. Conventionally, crosshole electromagnetic tomography may involve varying the positions of the receiver and transmitter tools during the gathering of the measurement data so that a given measurement may be associated with a particular transmitter position and a particular receiver position. After the measurements are taken, a crosshole survey may be developed based on the receiver and transmitter positions and the measurement data.
A challenge in using crosshole electromagnetic tomography is accurately determining the receiver and transmitter positions. Traditional techniques to determine these positions typically involve manual data fitting, which may consume a considerable amount of time.
Thus, there is a continuing need for better ways to determine the relative positions of receivers and/or transmitters that are used in crosshole electromagnetic tomography.